Spent a weekend on a DIY desk once, never again. It ended up costing more in time than money saved. Why not just buy one that works right out of the box?
You mentioned building your own saves cash and fits your space, and that's exactly why I went DIY too. I used some old shelf brackets and a solid door from a reuse store for the top. It cost me maybe forty bucks total, and now I have a desk that's the perfect height for my weirdly shaped corner. Like @joel_wilson said, the custom fit is unbeatable. Have you found any good plans online for the frame?